Bump because I want to hear what would have caused this issue as well.

 

in thinking about it...i guess you could cause this issue by accelerating while trying to put it into 4H. The previous owner might have done this...then decided to trade in not knowing what was wrong. I got the truck and it came with a warranty from the dealer so I made out fine. Thats just my guess.

 

I don't know what the dealer found, but "banging" noise[s] doesn't sound like a hub/IWE issue to me. Those are typically more of a grinding or buzzing sound. Maybe the dealer is going for the cheaper repair option first. The original solenoid (which you said had been replaced) may have damaged the hubs/IWEs too. Let us know...

 

maybe...I don't know...I only had the truck for a week. All I do know is that it doesn't sem to be a vacum issue. The vacum is good. When the hubs are under a load (accelerating) it bangs at they are trying to engage in 4H...as soon as you let out of the throttle...they don't engage either...but when you hit the gas...they engage and then fall our and then engage again..had my cousin, who's a mechanic check it out before I dropped it at ford and he said it was definitely a hub issue. Now ford says that both had to be replaced...I don't see how thats a cheaper option than replacing vaccum lines...